text: Recovery of nutrients from excreta in non-sewered sanitation systems was addressing the sanitation problems in settlements in Europe and elsewhere and was contributing to securing agricultural productivity. However, the practice did not become the dominant approach to urban sanitation in the 20th century and was gradually replaced with sewer-based sanitation systems without nutrient recovery (apart from agricultural reuse of sewage sludge in some cases) – at least for cities that can afford it.
  There were four main driving factors that led to the demise in the recovery and use of excreta and greywater from European cities in the 19th century:
  * Growth of urban settlements and increasing distance from agricultural fields.
  * Increasing water consumption and use of flush toilet: Water flushing greatly increased the volume of sewage, at the same time diluting the nutrients, making it virtually impossible for them to be recovered and reused as they previously were.
  * Production of cheap synthetic fertilizers, making any efforts to recover and reuse the nutrients and organic material from the large volumes of sewage obsolete.
  *  Political intervention as a consequence of the perceived need for a change with regards to how to deal with odorous substances: Up until the end of the nineteenth century the dominant theory on the spread of illness was the miasma theory. This theory stated that everything that smelled had to be gotten rid of because inhaling bad smells was thought to lead to illness. 
  The use of (odorous) animal manure in agriculture has continued through to this day, probably because the odor of manure was not thought to contribute to human illnesses.
  The recovery of nutrients from wastewater still continues in two forms: 
  * Wastewater reuse or resource recovery: Use of raw, treated or partially treated wastewater for irrigation in agriculture (with the associated health risks if it is done in an improper way which is often the case in developing countries); and 
  * Application of sewage sludge to agricultural lands which is not without controversy in many industrialized countries due to the risks of polluting soils with heavy metals and micropollutants if not managed properly (see biosolids).